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The petcock in my radiator has both ears broken and half of the fitting nut broken. I suspect that the previous owner tried to remove it and broke the fitting. The radiator doesn't leak but I would like to remove the broken petcock and install a new one. Needless to say that this is an original radiator and I'm concerned about damaging it when a replacement is $$$! I'm concerned that the fitting and radiator are similar metals and the fitting is probably galled in the radiator threads. Any ideas? What about drilling it out?
The petcock assembly used on GM #3155316 aluminum radiators is a special petcock used for aluminum radiator application only and of GM #3150906. This petcock used a 1/4" NPT aluminum fitting instead of the brass type used in most other applications. The reason for this construction is to prevent DIS-SIMILAR metal(galvanic) corrosion from damaging the radiator. You will note that, for the same reason, the aluminum radiator installation was otherwise designed to prevent the metal of the radiator from directly contacting any other chassis metal. Rubber insulator mounts were used top and bottom to assure this. Steel fan shrouds had a rubber seal on the radiator-facing side.
The aluminum petcock fitting is quite soft. Whether or not galling has occurred, it may be difficult to remove. However, I think that it's worth a shot if you are careful about NOT applying excesive torque. Make sure that you use a tubing wrench for this fitting to give you the best chance at not rounding it off. Apply a reasonable amount of force; if the radiator gives way with a reasonable amount of force at this point, it was probably not long for this world, anyway.
If this fails, your only option will be drilling it out. Once you get the drain cock, inner portion drilled away, use gradually increasing drill sizes until the remaining aluminum fitting is paper thin. Then, you should be able to pick it out with a sharp stylus or an awl. The aluminum fitting will drill out VERY easily. With sharp drills, it will be like a hot knife through butter.
After I removed my original 66 SB radiator, I noticed that the drain at the bottom was damaged. I was taking it in to have it flushed out and the owner, who happens to own a mid-year himself, put a set of vice grips on it, gave it a twist and it came right out. Gary
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